1. Field of the Invention
The present invention relates to a planetary mixer which is used in various fields such as chemistry, medicines, electronics, ceramics, foods and feed, and in which stirring vanes formed into a frame shape (a frame-shaped blade) perform planetary motion in a tank (a vessel or a stirring tank), by which solid/liquid type treatment materials can be subjected to a treatment such as stirring, blending, mixing/kneading or kneading.
2. Background Information
Treatment operations such as stirring, blending, mixing/kneading or kneading of solid/liquid type treatment materials of from a low viscosity to a high viscosity (up to 3,000 Pa·s) regardless of oiliness or aqueousness, have been mainly made in a batch system by a planetary mixer, for example, a bi-axial mixer (such as a mixer having two frame-shaped stirring blades), a tri-axial mixer (such as a mixer having three frame-shaped stirring blades, or a mixer having two frame-shaped stirring blades and one turbine blade in combination), or a quad-axial mixer (such as a mixer having two frame-shaped stirring blades and two turbine blades), in which plural frame-shaped stirring blades 1 perform revolution and rotation to move throughout a tank 2 as shown in FIG. 4. The frame-shaped stirring blade may usually have a structure wherein a substantially rectangular frame having a vertical side portion 3 and a horizontal side portion 4 is formed by rods having a cross section of substantially triangle shape (for example, reference may be made to Patent Document 1) and a cross section of substantially hexagonal shape (for example, reference may be made to Patent Document 2), and an edge face (an acute angle section) 7 formed by slope faces 5, 6 of the vertical side portion 3 is directed outwardly as seen from the center of the stirring blades, as shown in FIG. 5. When the frame-shaped stirring blade turns, the edge face 7 of the vertical side portion 3 comes close to the inner wall of the tank 2, and shearing stress is applied to treatment materials between the edge face and the inner wall of the tank to conduct the treatment such as a mixing/kneading operation. Accordingly, in the case of a batch system, the opportunity of applying the shearing stress to the materials between the frame-shaped stirring blade and the inner wall of tank (stirring tank) is non-continuous. In a mixing/kneading machine of which the frame-shaped stirring blade traces a planetary motion track, the opportunity is two times per one rotation of the frame-shaped stirring blade.
Observation will be made below about the powder at the time of charging which flows around the periphery of the vertical side portion of the frame-shaped stirring blade and between the vertical side portion and the inner wall of the tank, and the flow of the materials at the time of mixing/kneading. As shown in FIG.5, firstly, when the vertical side portion 3 of the frame-shaped stirring blade 1 moves toward the arrow 8 in FIG. 5 (circumferential direction), a part of the materials in the tank is pressed by a forward side face 9 located at the front face side relative to the direction of movement of the vertical side portion 3 and made to flow in an outward direction (radial direction) along a forward slope face 5 at the front face side located next to the forward side face 9. The flowing materials which has reached the front end of the slope face 5 enters a gap 10 with the inner wall of the tank 2, and are then compressed between the inner wall of the tank and the edge face and the shearing stress is also applied thereto when the stirring blade turns to conduct stirring, blending, mixing/kneading, kneading, etc. The materials that have passed the gap 10 between the front end of the stirring blade and the inner wall of the tank are released from pressure, and expanded along a rearward slope face 6 at the rear face side relative to the direction of movement.
On the other hand, the materials which have blown against the forward side face 9 and not flowed in the direction towards the inner wall of the tank (radial direction) flow in a circumferential direction (tangential direction) by turning from the forward side face 9 of the vertical side portion 3 toward an inner side face 11 inwardly (rearward), and at this stage, a phenomenon wherein adhered (fixed) materials 13 of the treatment materials are formed is observed on the forward side face 9, inner side face 11 and rearward side face 12. Particularly, in the frame-shaped stirring blade 1, since the vertical side face 3 is formed to have a cross section of substantially triangle shape or substantially hexagonal shape so that the edge face (acute angle section) 7 formed by the slope faces 5, 6 faces outwardly as mentioned above, the inner face 11 forms a flat plane portion and both ends of the inner face 11 are connected continuously to the forward side face 9 and the rearward side face 12 via a right angle corner, respectively. Accordingly, along the flow of the materials flowing in the circumferential direction (tangential direction), negative pressure directed to the flat plane portion or stagnation phenomenon occurs, and as the results, the materials are drawn toward the corner of the inner face 11 and the rearward side face 12 and tend to adhere thereto as shown in FIG. 5.
As mentioned above, when the materials adhere (fix) to the frame-shaped stirring blades, it is required to stop the mixing/kneading operation and scrape the adhered materials 13. This scraping operation is accompanied with dangers. If such scraping operation is not conducted, it becomes difficult to conduct homogeneous treatment. Particularly in a case of a treatment process including a step where the materials are subjected to strong kneading and then dilution, blob and lump are likely formed and the incorporation of lump, etc. during the dilution may cause failure of quality. Further, since such scraping operation is necessarily conducted halfway in the operation, the operation cannot be carried out continuously. Furthermore, since the tank cannot be tightly closed until completion of the scraping operation, in a case where a volatile organic solvent is used, problems of environmental pollution may sometimes be caused by diffusion of the solvent.